﻿Interfaces between
the photoactive layers and electrodes play critical roles in controlling the
performance of optoelectronic devices. Herein, a novel nonconjugated polymer
additive (nPA), poly(2-vinylpyridine) (P2VP), is reported for modifying the
interfaces between the bulk-heterojunction (BHJ) and cathode/metal oxide (MO)
layers. The P2VP nPA enables remarkably enhanced power conversion efficiencies
(PCEs) and ambient stability in different types of polymer solar cells (PSCs).
Importantly, interfacial engineering can be achieved during deposition of the
P2VP nPA-containing BHJ active layer via simple, one-step solution processing.
The P2VP nPA has much higher surface energy than the BHJ active components and
stronger interaction with the surface of MO, which affords spontaneous vertical
phase separation from the BHJ layer on the MO surface by one-step solution
processing. The self-assembled P2VP layer substantially reduces the work
function and surface defect density of MO, thereby minimizing the
charge-extraction barrier and increasing the PCEs of the PSCs significantly,
i.e., PTB7-Th:PC71BM (10.53%→11.14%), PTB7:PC71BM (7.37%→8.67%), and PTB7-Th:P(NDI2HD-T) all-PSCs (5.52%→6.14%). In addition, the lifetimes of the PSCs are greatly improved
by the use of the P2VP nPA.